A change order is initiated by the SCA whenever field conditions are encountered which differ from what is shown by or can be reasonably inferred from the documents issued for bid. The process is also initiated when the SCA issues modifications to the bid documents after the bid is opened and the construction award is made.  The SCA acknowledges a change by issuing a Notice of Direction (NOD). The contractor submits a proposed cost for the work, negotiations take place and after a settlement is reached, a change order is issued and executed. It is important to note that in accordance with the contract, to avoid adversely affecting construction progress, the contractor must immediately proceed with the work described by the NOD.